ABSTRACT
First Person is a series of interviews with the first authors of a selection of papers published in Journal of Cell Science, helping early-career researchers promote themselves alongside their papers. Tetsuo Mioka is first author on ‘ Characterization of micron-scale protein-depleted plasma membrane domains in phosphatidylserine-deficient yeast cells’, published in JCS. Tetsuo is an assistant professor in the lab of Kazuma Tanaka at the Division of Molecular Interaction Institute for Genetic Medicine, Hokkaido, Japan, where he is involved in characterization of a novel plasma membrane domain generated in PtdSer-deficient budding yeast cells.
Tetsuo Mioka
How would you explain the main findings of your paper in lay terms?
In general, in the plasma membrane (PM), proteins are distributed everywhere without any significant bias. However, in a budding yeast mutant that is unable to produce phosphatidylserine (PS), one of the major phospholipids, we found that a strange region with almost no protein distribution appears in the PM at high temperatures. Such a heterogeneous distribution of proteins without special diffusion barriers had never been seen in the PM of living cells. We named this special region the ‘void zone’ and analysed it. We clarified some of the conditions necessary for the formation of the void zone, and also discovered a new phenomenon in which the vacuole, the degradation apparatus in the cell, contacts the void zone of the PM.
Were there any specific challenges associated with this project? If so, how did you overcome them?
I had observed early on that a few specific membrane proteins were not distributed in the void zone. However, the question ‘Are all membrane proteins excluded from the void zone?’ was unlikely to be solved by conventional fluorescence microscopy. We then asked our collaborators (Takuma Tsuji and Toyoshi Fujimoto) to observe the cell surface by electron microscopy using the quick-freezing and freeze-fracture labelling (QF-FRL) method. As a result, we were able to obtain images that clearly showed the depletion of membrane proteins in the region that seemed to correspond to the void zone, strongly suggesting that most membrane proteins cannot enter the void zone.
Image of the void zone. In PS-deficient cells (cho1Δ), the void zone, a protein-depleted region, is present in the plasma membrane at high temperatures (left panel; arrowheads). Vacuoles tend to contact with the void zone (right panel).
Image of the void zone. In PS-deficient cells (cho1Δ), the void zone, a protein-depleted region, is present in the plasma membrane at high temperatures (left panel; arrowheads). Vacuoles tend to contact with the void zone (right panel).
When doing the research, did you have a particular result or ‘eureka’ moment that has stuck with you?
There were two moments in particular when I felt ‘eureka’. The first was when I happened to discover the void zone in my PhD course. I was looking at my microscopic images and noticed that some cells were strangely devoid of fluorescent signals. I observed the cells again and confirmed the strange phenotype. I was very excited that this could be something new. After I finished my PhD, I started to analyse the void zone. One day, I noticed from DIC images that void zones and vacuoles tended to be in close proximity. I was very surprised and excited when I confirmed this phenomenon by staining the vacuoles the next day.
What's next for you? (If you are planning on leaving academia, please tell us why!)
Although I am leaving Hokkaido University, where I conducted this research, I will continue my research on lipids and membranes using budding yeast at a new university (Aoyama Gakuin University).
Tell us something interesting about yourself that wouldn't be on your CV
While I was focusing on this void zone research, I was able to get married and have a baby, so this research article is very memorable and unforgettable. I am very grateful to my wife for her support.
Tetsuo Mioka's contact details: Division of Molecular Interaction Institute for Genetic Medicine, N15 W7, Kita-ku, Sapporo, Hokkaido 060-0815 Japan.
E-mail: [email protected]
